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' No Drawing.

,35 chemical equations:

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' c1 on 7 HO -0 Q Patented Feb. 3, 1931 i UNITED stares ons, BY MEs ASSIGNMENTS, 'ro NEWPORT cH'EivrIcAL ooEroRA TIoN, A coRroBA- ron 0 DELAWARE This invention relatesto a method of pre- 'paring purpurin, otherwise referred to a 1-3-4 tri-hydroXy. anthraquinone.

v It is an object of this invention to provide U 'l a simple, efiicient and practical method for the preparation of purpurin, which is a valuable intermediate for dye stufis.

Other and further important objects of this invention will be apparent from the 011 19 lowing description and the appended claims.

Purpurin or 1-3-4 tIl-hYdIOXY anthraquinone has been prepared generally by the oxidation of alizarin or quinizarine.

We have now discovered that purpurin can be easily prepared by the hydrolysis of 3-chloro-quinizarine, namely l-4 dihydroxy If 3-chloro-quini- S-chloro anthroquinone. zarine be subjected in the presence of concentrated sulphuric acid and boric acid at an 20 elevated temperature for a prolonged period t of time it is hydrolized'to form purpurin. We have further observed that purpurin may be prepared in one continuous operation in the same reaction mass. These reactions are probably best expressed by the following temperatures below 190 0., but is-accelerfrom 8-4 dichloro phenol by firstpreparing anuary 10,1928, followed by the hydrolysis of the chlorine group to a hydroxyl group ATE -OFFIJC'EY HENRY E; LEE ANDIVAN GUBELMANm oEsoUTn MILWAUKEE, WISCONSIN, ASSIGN- PROCESS OF'PREPARI N G BURPUBI-N YA neation filed SeptemberZ, 1927,). serial 'No. 217,300.

ated raising the temperature toKabout 220 C; The 1-3-4 t'rihydroxy anthraquinone obtained directly by thisprocessis a reddish brown powder having a melting point of 248-250 C. After a single.recrystallization from alcohol, substantially pure. 1-3-4 tri'-' hydroxy I anthraquinone 'is obtained havinga melting point of 254-255" (1., which corresponds to themelting point given by Ullmann in thefEnzyklopadie der Technis'chen Chemie, edited by Urban and Schwarzen- 1-3-4 trihydroxyanthraquinone 1s very spar-- tion. {It dissolves inalcohol impartingt'o it berg 1914 in Berlin volume page a 'y'ellowish to'reddis'h'yellow color. Indilute caustic}sodai'solution it is readily soluble lmparting to the 'solutio'n a purplish red color, whichis' completely discharged by the I action oflightand airi 'f It is'sol'uble in 'concentrated sulphuric acid with a rose red v color.-

the addition of alum to a sodium carbonate solution-"of the procluct,the characteristic red Ylalieof purpurin is formed."

7 Without limiting our invention to any particular; procedure, the "following examples, in which parts by; weight are given, will serveto illustrate preferred embodiments of our invention':

suiphurie acid menohydmte, parts-of v I 8o Ewairtple 1.'A""niiXture of1900- parts of boric acid, and .300 partsof' phthalic anhy- I dride is heated to 195C. Into this mixture areeimrgedioo' parts of"3,4-dichloro-phenol. The reaction niiXtureisheldfor 4 hoursjat 195 06200" Thetemperature is now raised to 220 C. andheld remoteness"; The'mass'is nowf co ole d to I601to170GLand poured into 38,000 parts or cold wate1*-. The precipitated acid ybe driedatlOO o. in vacuo. V 1 a a Example, inixtu're ot'l900 parts moiiohydrate,1l0 partsof boric acid-and 300 parts of phthalic anhydride is heated'to1959: V G. '-There'isfthen-ad'decl to this mixture 100 parts of 3,4-d'ichloro-phenol, and'a temperature of 195 to 200 C. maintained for 4 hours. 95 parts of water are now added and the temperature raised to 220 C. and held at this then maintained for 4 hours.

point for 20 hours. The isolation of the product is made as in. Example 1.

Example 3.-A mixture of 1900 parts of sulphuric acid, containing 5% free S0 11 0 parts of boric acid, 300 parts of phthalic anhydride is heated to 195" C. To this mixture are then added 100 parts of 8,4-dichloro.-..

phenol. A temperature of 195 to 200 C. is 190 parts of water are now slowly added and the temperature raised to 220 C. and held at 220 C. for 20 hours. The isolation of the product is madeas in Example 1.

Example .4.A mixture of 1900 parts of I monohydrate, 110 parts of boric acid,"136

parts of 3-chloro-quinizarine is heated to a temperature of 220 C. The temperature of 220 C. is maintained for 20 hours andthe isolation of the product made as in Example 1. c

' The yield of purpurin obtained by the procedure described in any one of the examples is substantially equal to that theoretically ex pected. The quality of the product withoutfurther purification has been sufiiciently high for technical uses. a

We are aware that numerous details of the process may be .varied through a Wide range,

for instance, the mixture of boric acid,

phthalic anhydride, sulphuric acid, and 3,4-

dichloro-phenol may be made at lower temperatures than those specified in the examples and the mixture gradually heated up to the reaction temperature; the proportion.

of the reacting substances may bevaried to a large extent without greatly afiecting the product; or similar results may be obtained 7 by a variation in the temperatures and time intervals specified. ,We, "therefore, do not propose to limit the patent granted hereon otherwise than necessitated by the prior art and as defined by the appended claims.

' We claim as our invention:

1. The process of preparing purpurin, which comprises hydrolyzing 3-chloro-qu1n1- zarine.

2. The. process ofpreparing purpurin,

which comprises hydrolyzing 3-chlor0-qui-' 1 l nizarine in the presence of sulphuric acid at an elevated temperature.

7 Y 3. The process of preparing 'purpurin,

which comprises'heating a reaction mixture containing 3-chloro-qu1n1zar1ne' and formed from phthalic anhydride, 3,4 -dichloro-phenol, sulphuric acid and boric acid at a temperature above 190 C. for a prolonged-period of time.

4. The process of preparing purpurin, which comprises heating a solutionof3-chloro-quinizarine in concentrated sulphuric acid at a temperature of about 220 C. for a "prolonged period of time. 

